Peptide–peptide and protein–peptide interactions in mixtures of whey protein isolate and whey protein isolate hydrolysates

The extent of aggregation in whey protein isolate (WPI) hydrolysates induced by Bacillus licheniformis protease was quantified as a function of degree of hydrolysis (DH), temperature and ionic strength. The capacity of the hydrolysates to aggregate added intact protein was also studied. The amount of aggregated material and the size of the aggregated peptides were measured by nitrogen content and size exclusion chromatography, respectively. Aggregation increased with DH up to the practical end point of hydrolysis (DH 6.8%). The aggregates formed under the various conditions studied consisted of peptides with masses ranging from 1.4 to 7.5 kDa. The hydrolysates were also able to aggregate added WPI. The additional amount of aggregated material increased with increasing DH. Peptides involved in peptide–peptide interactions were also involved in protein–peptide interactions. It is hypothesized that hydrophobic interactions dominated peptide–peptide interactions, while protein–peptide interactions depended on the balance between hydrophobic attraction and electrostatic repulsion.